**1. Introduction**

Since the 20th century, along with the acceleration of global urbanization and industrialization, the continued large-scale exploitation of land resources has been accompanied by environmental problems, such as the crowding of ecological space by urban construction land, atmospheric pollution, water pollution, and ecological imbalance [1–3]. Since the reform and opening up of China in 1978, urbanization and industrialization have advanced rapidly. At the end of 2018, 59.6% of China's land was urbanized, and China has entered a period of steady urbanization [4,5]. In this context, structural imbalances in land use have come to the fore, the contradiction between production-living-ecological space (PLES) has become increasingly prominent, and land use is facing enormous pressure and challenges [6,7]. Therefore, to promote regional sustainable development and the effective and efficient application of land space, it is necessary to reasonably allocate limited spatial resources [8–10]. Integrating the spatial functions and land use structure under the PLES linkage and promoting the coordinated development of the quantitative structure and spatial layout of the PLES has become an urgent issue to be addressed [11,12].

Ecosystem services (ES), as a bridge between natural ecosystems and human well-being, are the various benefits that humans derive directly or indirectly from ecosystems [13,14].

**Citation:** Fu, X.; Wang, X.; Zhou, J.; Ma, J. Optimizing the Production-Living-Ecological Space for Reducing the Ecosystem Services Deficit. *Land* **2021**, *10*, 1001. https:// doi.org/10.3390/land10101001

Academic Editors: Dong Jiang, Jinwei Dong and Gang Lin

Received: 18 August 2021 Accepted: 17 September 2021 Published: 23 September 2021

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Ecosystem services depend on the interactions and feedback between ecological and socioeconomic factors [15,16]. Humans manage ecosystem processes by modifying ecosystem components and structures to provide ES that better meet their needs [17,18]. A common way of doing this is improving human well-being by changing land use/cover, e.g., converting other lands to cropland can improve food production service. The conversion of arable land and grassland into forest land can improve water yield services, soil conservation services, and carbon sequestration services, etc. [19]. The gradual deepening and formation of the concept of ES provides a vehicle for interlinking the elements of human-land system coupling [20,21]. As a result, the concept of ES is now becoming increasingly important at the land management level [22,23].

With the deepening of ES research, a large number of researchers have begun to focus on both the ES supply (i.e., the capacity of ecosystems to provide ecosystem goods and services to humans) and the ES demand (i.e., the sum of ecosystem goods and services used or consumed by humans) [24,25]. The gradual intensification of global climate change, environmental pollution, and human-land conflicts have led to changes in ecosystem structure and function, affecting the supply capacity of ES [26,27]. Meanwhile, the increasing level of urbanization and industrialization has led to the emergence of a large number of ES demand aggregation centers [28,29], further exacerbating the mismatch between ES supply and demand. Incorporating ES supply and demand into ecosystem assessments can improve the policy relevance and practical application of the ES concept in land management. It is also conducive to achieving ecological security and safeguarding human well-being [30,31].

There is often a desire to maximize the ES supply through land management to reduce mismatches and shortages, but a major challenge is to integrate analysis to avoid unnecessary trade-offs in ES [32,33]. In this context, exploring spatial mismatches between ES supply and demand associated with urbanization-related land use is crucial for the proper integration of ES into land management strategies [34]. Many studies have considered both ES supply and demand and have identified potential mismatches between ES supply and demand at multiple scales [35]. The challenge is that most ES assessments have not yet been effective in influencing land management decisions and, in particular, lack holistic considerations [36,37]. The PLES covers the spatial range of activities of human social life and is the basic vehicle for human economic and social development [38]. The three are both independent and interrelated, with symbiotic integration and constraining effects, and the collaboration of PLES functions can produce a synergistic effect in which the overall function is greater than the sum of the partial functions [39]. The PLES optimization belongs to the problem of optimizing the allocation of national land resources. Based on land characteristics and land-use system principles, the structure and direction of land resource use are arranged, designed, combined, and laid out at a hierarchical level on a spatial and temporal scale to improve the efficiency and effectiveness of land use, maintain the relative balance of land ecosystems, and realize the sustainable use of land resources [40]. The main theoretical support for current PLES optimization comes from the theory of regional resource and environmental carrying capacity and the theory of coupling urbanization and ecological environment [41,42]. This study focuses on the consideration from the perspective of ecosystem services, and it is a new attempt to apply the assessment of ecosystem service supply and demand to the optimization of PLES.

The Yellow River Basin, an important ecological barrier, straddles three regions in the east, central, and west of China and is an ecological corridor connecting the Qinghai-Tibet Plateau, the Loess Plateau, and the North China Plain. Although breakthroughs in ecological construction and environmental management have been made in the Yellow River Basin in recent years, the fragile ecological environment, water scarcity, and water environment problems are outstanding. especially in the middle and lower reaches of the Yellow River, which have undergone rapid urbanization over the past decades, leading to huge changes in the spatial pattern of land use, accompanied by huge landscape changes and related degradation of ES. Therefore, this study takes the Yellow River basin as an

example to explore the spatial patterns of ES supply and demand and the response to PLES changes and to identify optimization areas through response thresholds to provide optimization strategies for land use at multiple scales.

Land use optimization is a complex concept [43]. This study has envisaged an ideal area where optimal PLES management reduces ES deficits and mismatches, to which the land use pattern of the remaining areas should be as close as possible. The basic optimization four steps included: (1) classifying production-living-ecological spaces based on land use types; (2) choosing key ES, quantifying ES supply and demand, and identifying spatial mismatches; (3) identifying the impact of PLES on the spatial mismatch of ES and thresholds; (4) determining the direction of optimization and proposing optimization solutions for different spatial scales.

The selection of key ES was based on the following principles: (1) spatially quantifiable mapping; (2) consistent with the focus of regional governments and residents; (3) better representation of the coupling mechanisms between different ES; (4) availability of measurement data. In this study, the carbon sequestration service, water yield service, soil conservation service, and grain production service were selected as indicators for measuring the ES supply and demand in the Yellow River Basin to minimize the deficit and mismatch of these four ES and carry out corresponding PLES optimization.

### **2. Materials and Methods**
